Interface Essential

Business

Images Photography

Money Shopping

Programming

Computer Devices

Phone

Mail

Map Travel

Food Drink

Nature Ecology

Entertainment

Shipping

Culture

Health

Work Education

Artificial Intelligence

Arrows

Streamline 3.0

Ultimate

Core

Flex

Sharp

Plump

Micro

Freehand

Streamline Material

Nova

Cyber

Streamline Vault

Logos

Pixel

Google Material

Tabler

Remix

Feather

Iconoir

Carbon

Solar

Lucide

Brand Logos

Bootstrap

Atlas

Unicons

Ionic Icons

Phosphor

MingCute

Font Awesome

Majesticons

Mynaui

Radix

Heroicons

Flagpack

Outlined Line - Streamline Material Free

Stroke Outside Inside

Text Formatting

Rounded Line - Streamline Material Free

Sharp Line - Streamline Material Free

Outlined Fill - Streamline Material Free

Stroke Outside Inside Fill

Sharp Fill - Streamline Material Free

Plump Line

Inside Stroke

Vectors

Plump Pop

Plump Flat

Plump Gradient

Plump Remix

Plump Duo

Plump Neon

Plump Solid

Core Line

Sharp Flat

Sharp Remix

Sharp Line

Sharp Pop

Sharp Duo

Sharp Neon

Sharp Solid

Sharp Gradient

Flex Solid

Flex Remix

Flex Line

Flex Gradient

Flex Neon

Flex Flat

Flex Pop

Micro Solid

Micro Line

Flex Duo

Core Gradient

Core Neon

Core Duo

Core Pop

Core Remix

Core Solid

Cyber Line

Border Inside

Alignment

Cyber Duotone

Freehand Duotone

Transform Inside

Transform

Ultimate Colors

Ultimate Bold

Ultimate Light

Ultimate Regular

Ultimate Duotone

Rounded Line - Streamline Material

Sharp Line - Streamline Material

Outlined Line - Streamline Material

Border Inside Horizontal

<p>Flex is all about the curves. Its smooth curves brings fluidity and dynamism to your designs with a modern appeal.&nbsp;The Duo style is perfect for projects that require differentiation between actions, using color to convey meaning effectively. It also allows you to customize the line thickness.&nbsp;All Flex Duo icons are designed on a 14px grid with a 1px default stroke and two customizable colors.</p>

**Summary**: Flex's two-color system — 1px organic line with dark periwinkle blue primary and lighter blue secondary, adding colour depth and structured hierarchy with the flowing visual quality unique to the Flex family. Organic curves keep the two-color system from reading as corporate despite the blue palette, making it softer and warmer than equivalent duo systems in more geometric families. The tone signals organic structure: "we differentiate through flow, not rigidity." Best for modern SaaS wanting a two-tone icon system with organic visual quality, products with a brand blue where the duo adds depth without imposing rigid geometry, and feature and documentation sections.

**Last updated**: 2026-04-23

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## Fit & Recommendation

### Primary use cases

- Modern SaaS wanting a two-tone icon system with organic visual quality
- Products with a brand blue where the duo treatment adds depth without rigid geometry
- Feature comparison, help, and documentation sections

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## Brand & Cultural Identity

### What it communicates

> "We differentiate through flow, not rigidity."

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## Visual & Technical Specs

### Visual properties

| Property | Value |
|----------|-------|
| Stroke weight | 1px |
| Fill | None (line only) |
| Corner treatment | Smooth fluid curves |
| Color | Dark periwinkle blue + lighter blue secondary |

### Emotional Scores

Flex Duo is somewhat warm — the blue two-color palette is cool, but organic 1px curves soften the coolness compared to geometric duo sets. It is among the softest sub-styles in the catalog — the 1px organic curves in a two-color system remain visually soft despite the structural intent. It is somewhat warm on friendliness — the two-color system adds structure while organic shapes keep it from reading as corporate. It is near neutral on playfulness leaning slightly serious — colour differentiation reads as functional and considered rather than playful or severe. On its human↔mechanical character, it is one of the more human-feeling sub-styles in the catalog — the two-color system adds semantic structure while organic curves retain a natural quality.

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## Pairing & Compatibility

### Typography pairing

- **Primary**: Plus Jakarta Sans — humanist warmth appropriate for the flowing two-color system
- **Alternative**: Outfit — modern humanist, pairs with the blue duo
- **Body**: Inter Regular
- **Avoid**: IBM Plex Sans — engineering register creates personality conflict with organic curves


<p>Flex is a fluid icon family inspired by nature’s curves. It favors smooth, flowing forms. More organic than Core and subtler than the chunky Plump. Read about the <a href="https://blog.streamlinehq.com/flex/" rel="noopener noreferrer" target="_blank">design process</a>.</p>

Fluid icons

Inside Stroke icon - Flex Duo Set

Download Inside Stroke SVG vector or transparent PNG icon in Duo, Filled, Stroke style(s) for Sketch and Figma. It belongs to Flex Duo vectors SVG collection.